1. Field of the Invention
The present invention relates to a light source device for an endoscope, and particularly to a light source device which has an aperture for adjusting the amount of illuminating light supplied from a light source to an incident end surface of a light guide provided in the endoscope.
2. Description of the Related Art
An endoscope has a flexible conduit to be inserted into the internal organs of a human body, and a light guide is provided in the flexible conduit to transmit illuminating light. A light source device is connected to an end portion of the light guide. The illuminating light radiated from the light source device is led to an incident end surface and passes through the light guide to reach the distal end of the light guide, so that the illuminating light is output from the end surface of the endoscope to illuminate the diseased part. In the case of a fiberscope, the light reflected from the illuminated portion is led to an eyepiece provided in an operation unit, and in the case of an electronic endoscope, the reflected light is converted to an electric signal by a CCD provided in an end portion of the endoscope, and an image is displayed by a monitor device. Thus, the illuminated portion can be observed through the eyepiece or the monitor device.
In the light source device for an endoscope described above, an aperture for adjusting the amount of light, and a condenser lens for condensing the light onto an incident end surface of the light guide, are provided between the light source and the incident end surface. The aperture mechanism has a pair of flat plates which are placed on a plane perpendicular to the optical axis and are symmetrically disposed with respect to the optical axis. The flat plates are rotated about a rotation axis, which is parallel to the optical axis, so that the luminous flux is shaded horizontally from the outside peripheries of the section of the luminous flux. Accordingly, the degree of opening of the aperture is adjusted, so that the amount of illuminating light, or the brightness of the illuminated portion, is adjusted.
Usually, a xenon lamp is utilized as the light source for illumination of the endoscope, since it provides a high luminance and a lesser amount of heat. However, because of a convection of the xenon gas enclosed in the lamp, or an oscillation phenomenon and so on occurring in the electric discharge, the light radiated by the xenon lamp contains a swinging of the amount of light in an area above the center of the luminous flux, and thus an illuminating light, in which the amount of light is uniform in the section of the luminous flux, cannot be obtained. When the aperture is almost fully open and the amount of light is relatively large, the swinging does not generate a substantial problem. Conversely, when the aperture is closed to reduce the amount of light, the swinging becomes remarkable, and this swinging may interfere with the observation of the illuminated portion through the eyepiece or the monitor device.
Therefore, an object of the present invention is to provide a light source device for an endoscope, which reduces an influence of the swinging of the amount of light even when the amount of light is reduced by the aperture mechanism, so that an illuminating light, in which the amount of light is uniform in the section of the luminous flux, can be obtained.
According to the present invention, there is provided a light source device for an endoscope, comprising a light source and an aperture mechanism.
The light source radiates an illuminating light to an incident end surface of a light guide of the endoscope. The aperture mechanism is disposed in an optical path formed between the light source and the incident end surface. The aperture mechanism has a pair of aperture blades, which are perpendicular to the optical axis of the illumination light and rotatable about a rotation axis which is parallel to and located above the optical axis, and a protruding portion integrally formed on an inside periphery of at least one of the aperture blades. The inside periphery faces the optical path. The aperture blades are rotated, so that the optical path is shaded horizontally from the outside peripheries thereof by the aperture blades. The aperture blades are further rotated, so that an upper area above the center of the optical path is shaded by the protruding portion.
Preferably, the inside periphery of each of the aperture blades is linearly formed, and the protruding portion is a triangle of which the base is on the inside periphery of one of the aperture blades and the vertex is the peak of the protruding portion. This structure enables a simple manufacturing process of the aperture blades.
Further, according to the present invention, there is provided a light source device for an endoscope, comprising a light source and a shading member.
The light source radiates illuminating light to an incident end surface of a light guide of the endoscope. The shading member is disposed in an optical path formed between the light source and the incident end surface. The shading member is movable so as to shade the optical path. The shading member has a protruding portion integrally formed on an inside periphery thereof facing the optical path. The shading member is moved, so that the optical path is shaded horizontally from the outside peripheries thereof by the shading member, and the shading member is further rotated so that an upper area above the center of the optical path is shaded by the protruding member.
The light source comprises a xenon lamp, for example. Preferably, the shading member comprises an aperture blade, and the protruding portion comprises a protruding plate flush with the aperture blade. In this structure, the inside periphery may be linearly formed, and the protruding plate may be a triangle of which the base is on the inside periphery and the vertex is the peak of the protruding plate. This enables a simple manufacturing process of the aperture blades. Preferably, the shading member is rotated about a rotation axis which is parallel to and located above the optical axis of the illumination light.